An article that's worth reading about the connection between the politics of the 1930s and '40s and the political issues today: The Long Road of Eugenics: From Rockefeller to Roe v. Wade.
Before and even during World War II, a large part of mainstream society accepted the notion that whites were superior to other races, that Nordic whites were superior to other ethnicities, that aristocratic families were superior to poor people, as not only self-evident, but proven, by recently invented IQ tests and other new "scientific" methods. When birth control was new and Darwin's ideas not that old, a lot of people believed that the world would be a better place if only the poor and the dark-skinned and the handicapped could be stopped from breeding, and the aristocrats encouraged. A lot of the people who believed this were aristocrats themselves, and had political power. Some of them continued to believe it after the war. And they all were in favor of the sexual revolution, and the liberalizing of the laws that went with it.
It's worth keeping in mind, as those liberalized laws are debated today, what the original proponents thought that they would accomplish by passing them.
Details and documentary evidence are in that paper. I know that the author is credible and her research intensive, because she's a lawyer with a distinguished history of public service, and also my mother.